The first DTMF tone producing telephone was introduced in November of 1963 for the Bell System. Rotary phones interrupt electrical connections while spinning, and the resulting electrical pulses produced are interpreted as commands (such as 'dial this number'). The first commonly used telephony signaling system was pulse dialing. Signalling systems have evolved to fill that role - both for routing and dialing calls as well as for interacting with phone systems once connected. DTMF Tones for Automating Telecommunications InteractionsĪlmost as long as we've had telegraph and telephony systems, humans have needed a way to reliably interact with the system in a mechanical and reproducible way. Commonly used over telephone lines, DTMF tones are also commonly called Touch Tones. Although DTMF works in normal human voice range, the combination of inharmonic frequencies makes it hard for the human voice to impersonate.Īlthough mobile phone networks use digital signals instead of DTMF for direct dialing, DTMF is still used over mobile phones to navigate automated systems such as phone menus, voice menus and other advanced calling services.DTMF, or Dual-Tone Multi-Frequency tones, are in-band telecommunications signals sent over voice frequencies. The frequencies were chosen to avoid harmonics : no frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the frequencies. With DTMF, each keypress on your phone generates tones made of two specific frequencies. Over the years, DTMF has replaced Pulse dialing, the early type of telephone dialing in which short pulses were used to relay the dialed number.
Dual-Tone Multi-Frequency (DTMF) is the signal that you generate when you press an ordinary telephone's touch keys.
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